The present invention relates generally to methods and apparatus for time keeping, and particularly to methods and apparatus for time keeping in a system broadcasting time of day information by radio signal in an area including a time zone boundary.
Highly accurate time reference data is available by radio signal broadcast. Such information is used in a paging system using wristwatch paging devices. In such system, in addition to transmission of paging information, the wristwatch paging devices collect highly accurate time of day information from the paging broadcast protocol. Generally, such time of day information can be taken by the paging device as an accurate local time of day and used to update the time of day for the time keeping portion of the wristwatch paging device. In this manner, the paging devices intermittently receive an accurate time of day update and thereby maintain a highly accurate representation of time for display on the wristwatch paging device.
When the paging system reception area encompasses a time zone boundary, however, the local time of day reference provided in a given radio signal broadcast may not be accurate. Time display and maintenance is complicated when the paging system employs several broadcast facilities, each selectively used by the paging devices by use of a frequency agile receiver, distributed throughout a reception area. Signals broadcast from one facility in or near a given time zone may be received by paging devices in the other time zone. Furthermore, paging devices are likely to traverse the time zone boundary and could be in either one of the time zones at any given time. Thus, while transmission of local time of day information and intermittent updating of a time of day display in paging devices away from time zone boundaries can be as simple as collecting the local time of day information and updating the time keeping portion of the paging device, such procedure cannot be used across and near a time zone boundary. The paging devices should accurately represent local time of day with appropriate reference to a given time zone.
U.S. Pat. No. 5,089,814 issued Feb. 18, 1992 to DeLuca et al and entitled AUTOMATIC TIME ZONE ADJUSTMENT OF PORTABLE RECEIVER shows a portable receiver receiving a signal indicative of the location of the portable receiver. A memory element of the receiver associates the received signal indicative of location with a corresponding time zone. The receiver thereby determines the time zone of its location. Based on such information the device adjusts its time of day to meet the indicated local time zone standard. The disclosure of DeLuca et al does not, however, recognize problems in time keeping associated with a reception area including a time zone boundary.
Thus, it would be desirable to provide a method and apparatus facilitating time keeping by radio signal broadcast in and around a time zone boundary.